i have a car that is parallel or series. it depends on the position of the jumpers. in parallel you dont need a special charger. it takes 5 or 6 cycles to totally charge but then you can switch the jumpers and it runs in series. stock clone batteries will get about 8-10mins of runtime that way and still be fast.
i use my car that is wired in just series tho since i have a 4aa charger. theres an article on this in bit science.
bit science.